CD, welcome to the site.
You may have a couple of issues going on with your Red Oak. The spots may be fungal activity that is more or less innocuous. However, the big concern for me would be the information that your tree was losing its leaves prematurely. This can be a diagnostic for Oak Wilt as most other oak maladies do not cause premature leaf drop.
Your pictures don't show the entire leaf, but that piece of information together with marginal dessication (partially shown in your photos) brings about the concern of oak wilt, being that this is a red oak (highly susceptible species) in Texas (noted for Oak Wilt).
I would either take a leaf sample to a diagnostic lab or get someone on site familiar with this devastating disease to positively identify or rule it out. I would personally try to get someone who would not necessarily have a personal interest in simply taking the tree down, but would be more objective with the diagnosis and treatment regimen.
Sylvia
